Yeah, ascii is constant in quality (though one must not underestimate the impact of color choice!) while tiles vary between indecipherable and hard to tell what it is supposed to be.
But let me tell you a little story, how I really got hooked on Roguelikes.
I had this very, very, very boring job, and started playing ADOM to pass the time. Some folks wondered why I always had a DOS window open, a good part saw a black window, having no idea what a DOS window is, or would look like. Nobody ever suspected I was actually playing a Game, despite me, on numerous occassions shouting with Joy or Frustration, making heads turn in the whole office.
I think thats another advantage of ASCII over Tiles.